In many network environments, bandwidth is a scarce resource. Bandwidth may be limited by the connection infrastructure of the environment or the maximum transmission or reception speeds of devices on the network. Where bandwidth is scarce, significant improvements in transmission time can be achieved by reducing the size of files transmitted over a network.
Another common feature of networks, including the internet and the World Wide Web, is the transmission of redundant data. For example, often a client may request the same file on different days to observe any changes that have taken place. A large portion of the file data may be redundant in that it has already been transmitted to the user. For example, if the file is the web page of a newspaper, the headings and formatting information will remain constant. As another example, a client may load a file several times within a single hour, for example if the file is a web page listing updated sports scores. In this example, the only data that changes from viewing to viewing may be the scores themselves, and the team names, logos, and formatting will remain unchanged.
Several systems and methods already exist for taking advantage of this redundancy to reduce the size of transmitted files. Many web browsers store images from sites a user has already visited so that they do not need to be retransmitted if the user returns to the site. While this method is effective, it is typically limited only to standard image files, and cannot reduce file sizes for pages comprising large amounts of text, scripts, or formatting information. Many web sites utilize frames, applets, or scripts to control web pages so that only the portion of a page that has changed will be retransmitted. The drawback of this approach is that programming a site to use these techniques often requires substantial developer time and resources, and may require recoding previously existing files. Thus there exists a need for means to leverage the redundancy found in many network transmissions to reduce the size of transmitted files that may be easily applied to both presently existing and future files.